This invention relates to cathodoluminescent display devices. In particular the invention is concerned with cathodoluminescent display devices in which cathodoluminescent phosphor material is excited to emit light by low-velocity electrons, and is especially applicable to display devices such as low-voltage vacuum fluorescent display devices and low-voltage gas discharge display devices.
The term "low-velocity electrons" used herein means electrons having an acceleration potential in the order of 10 to 100 volts.
Heretofore, it has been common to use in, for example, low-voltage vacuum fluorescent devices, cathodoluminescent phosphor material comprising zinc oxide activated with zinc in view of its inherently conductive nature and the ability of zinc oxide phosphors to emit light in response to excitation by electrons accelereated between a potential difference in the order of 10 volts.
The color of the light emitted by such low-voltage vacuum fluorescent devices has been limited to a greenish white in view of the use of zinc oxide phosphor materials. Attempts have been made in recent years to use other phosphor materials in such low-voltage display devices by, for example, mixing zinc oxide with other phosphor materials, doping zinc sulphide to render the bulk of the material more conductive or by using an inherently more conducting phosphor material such as, for example, europium doped tin oxide in order to produce a wider range of colors.